Steam has many uses. For instance, steam is used in food processing, industrial processing, refining processes and chemical processes. Furthermore, steam can be utilized for power generation. Steam is also used to enhance oil and other hydrocarbon recovery. For instance, steam is used for recovery of heavy oils that have become somewhat entrapped within other soils or other constituents in geological formations and to cause the heavy oils and/or bitumen or other hydrocarbons to be more readily extracted and handled.
Depending on the use to which the steam is to be put, varying degrees of steam purity are required. Furthermore, some processes may have a high tolerance of some types of impurities and a low tolerance for other types of impurities. For instance, any non-condensable gases within a steam working fluid can cause a condenser of a power plant to work improperly unless a condenser is properly configured to remove such non-condensable gases (i.e. carbon dioxide or air). In food processing, contaminates which might be harmful to the consumer of the food are to be avoided if the steam comes into direct contact with the food. While non-condensable gases (unless in high amounts) are generally not a problem with food processing uses for steam.
In the prior art, the most typical way to generate steam is to utilize a boiler. Most boilers are indirect in that they combust a fuel and heat walls of a heat exchanger with the hot products of combustion. Water flows on the other side of the heat exchanger wall (typically within pipes) with the water in the pipes boiling into steam as the water passes through the boiler. The water is thus indirectly heating into steam. When all of the water has been boiled into steam, and no additional heat has been added, the steam is considered to be “saturated.” If the water has not been entirely boiled, but has some condensate water still therein, the steam is considered to be “wet.” If more heat has been added past the boiling point for all of the water, and all of the steam has been elevated in temperature above the boiling point for water at the given pressure, the steam is considered to be “super heated.” Depending on the temperature of steam required, and whether or not it is important that the steam be completely gaseous or benefits from being wet, the boiler is configured to raise the steam to the desired temperature and state. The steam can then be beneficially utilized.
More recently, a form of direct steam generation has been developed that is referred to as oxyfuel combustion. With oxyfuel combustion, a fuel containing hydrogen and/or carbon is combusted with oxygen (either pure oxygen or an oxidizer containing a greater proportion of oxygen than is present in air, i.e. about twenty percent). The hydrogen in the fuel reacts with the oxygen to directly form water. The temperature of such reactions is such that typically the water is formed in a gaseous state as super heated steam. Most typically with oxyfuel combustion, water (or some other diluent) is also added into a combustion chamber thereof to cool down the high temperature steam produced by combustion of the fuel with the oxygen. This additional water is directly heated into steam and is mixed with the steam generated by combustion of the fuel with the oxygen.
When the fuel also contains carbon, this carbon combines with the oxygen to also form carbon dioxide within the combustion chamber. Once the steam and carbon dioxide generated within the oxyfuel combustion gas generator are mixed with diluent cooling water, the stream exiting the gas generator is typically largely steam, with the carbon dioxide being a minority component. The degree of cooling required, the diluent flow rate, and the type of fuel influence these relative percentages of steam and carbon dioxide in the mixture exiting the gas generator.
Examples of such oxyfuel combustors and oxyfuel combustion systems are described in U.S. Pat. Nos. 5,680,764, 5,709,077 and 6,206,684, incorporated herein by reference in their entirety.
Steam and carbon dioxide can be relatively easily separated from each other, such as by providing a condenser cooling the mixture to the point where the water condenses into a liquid and the carbon dioxide remains a gas for effective separation of the carbon dioxide from the water. Also, many processes utilizing steam are tolerant to some amount of carbon dioxide along with the steam. Thus, direct steam generation through use of an oxyfuel combustion gas generator can be utilized for a variety of the processes which require steam. This invention is directed to variations on oxyfuel combustion gas generators and associated systems for effective utilization of direct steam generation oxyfuel combustion gas generators for the generation of steam for various uses in which steam is to be utilized.